| Global variable vs common block [message #19399] |
Thu, 16 March 2000 00:00  |
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marc schellens[1]
Messages: 183
Registered: January 2000
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Senior Member |
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hello everybody,
I have a very large program which uses common blocks (sorry David),
nowadays I don't like them any more (never liked them but lately I
discovered the DEFSYSV command :-). I used for the whole program just
one common block holding one structure (all the global data).
It was easy to change the suff to use a ('!named') global variable, and
at a first look everything seem to work fine.
So my question is: Is there something I have not thought about/do not
know were I can run into a limitation with this?
Wanna know this before I spent more time on the prog and eventually have
to change it back.
thanks,
:-) marc
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| Re: Global Variable [message #26830 is a reply to message #19399] |
Mon, 01 October 2001 08:33  |
Pavel A. Romashkin
Messages: 531
Registered: November 2000
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Senior Member |
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Martin,
The following URL points to a tiny file that does what you want.
http://spot.colorado.edu/~romashki/idl/single_set.sav
You can see basic description by typing
SINGLE_SET, /HELP
To set a global variable, use
SINGLE_SET, 'The_Name', My_State[, /NO_COPY]
To read it, use
My_State = SINGLE_GET('The_Name'[, /NO_COPY])
To kill it:
SINGLE_KILL, 'The_Name'
There is no limit on the number of named global variables.
If you did not keep track of global pointers using GET_HANDLE then
HEAP_GC will be able to kill them, as they exist as dangling references.
In this case, call to SINGLE_GET will re-create the named global
variable, but, of course, not its contents.
However, they are accessible via SINGLE_GET at any time.
Cheers,
Pavel
Disclaimer: I do not support using global variables. Provided procedure was
only written as an alternative to using COMMON blocks for those rarest
cases when widget programs are absolutely independent but benefit from
being aware of each other.
Martin Downing wrote:
>
> Reimar,
>
> If this is to be a global variable, do you have a cunning method of locating
> and identifying this variable off the heap?
>
> Martin
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| Re: Global Variable [message #26833 is a reply to message #19399] |
Mon, 01 October 2001 04:14 |
Martin Downing
Messages: 136
Registered: September 1998
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Senior Member |
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"Reimar Bauer" <r.bauer@fz-juelich.de> wrote in message
news:3BB83D11.5A58FC00@fz-juelich.de...
>
> The fourth way is to use Pointers
>
>
> value=10
> ptr=ptr_new(value)
>
> help, *ptr
>
> Reimar
>
Reimar,
If this is to be a global variable, do you have a cunning method of locating
and identifying this variable off the heap?
Martin
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| Re: Global Variable [message #26834 is a reply to message #19399] |
Mon, 01 October 2001 03:46 |
Miguel Ángel Córd
Messages: 11
Registered: March 2000
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Junior Member |
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Reimar Bauer wrote:
> Martin Downing wrote:
>>
>> First comment is to only use global variables sparingly, sometimes they are
>> appropriate but try not to rely on them to make programming simpler.
>> I know of three ways, the SYSTEM variables are fully global, and may be user
>> defined, COMMON BLOCK variables are shared between those routines which
>> include a
>> declaration for the common block, these are very suitable for those programs
>> where you cant find a way of writing your code without creating global
>> variables, but do not want the variables to be seen by any old routine.
>>
>> system variable eg:
>> ------------
>> IDL>filepaths = {tag:"FILEPATHS", bin:bin)
>> IDL>defsysv, '!fpaths',filepaths ; a variable for local paths
>>
>> now you can use this variable from anywhere in your code as:
>>
>> IDL> print, !fpaths.bin
>> d:\martin\bin\
>> ------------
>>
>> For common block variables you need a block identifier then a list of
>> variables in the block. Note that the order is all that is relevent and that
>> the first declaration defines the size of the block: eg
>>
>> pro foo
>> COMMON FOO_COMMON_VARIABLES, a,b,c,d
>> a = "first"
>> b="second"
>> c="third"
>> d="fourth"
>> print_foo
>> end
>>
>> pro print_foo
>> ; note later calls do not have to decare all block variables
>> COMMON FOO_COMMON_VARIABLES, d,c,var3
>> print, d
>> print, c,
>> print, var3
>> end
>>
>> the result of calling this procedure is demonstrates that there is no
>> association between variable names inthe common block just the variable
>> order.
>> IDL> foo
>> first
>> second
>> third
>>
>> ------------------------------
>> Lastly there is a *really* nice way of passing around all the 'global'
>> variables you need in your widget programs using get/set_uvalue which. This
>> is my favourite tip learnt from David's books so I shall leave him to
>> describe. In essence you call:
>> WIDGET_CONTROL, base, SET_UVALUE=info_structure
>> WIDGET_CONTROL, event.top, GET_UVALUE=info_structure
>>
>> cheers
>>
>
> The fourth way is to use Pointers
>
> value=10
> ptr=ptr_new(value)
>
> help, *ptr
>
> Reimar
>
> --
> Reimar Bauer
>
> Institut fuer Stratosphaerische Chemie (ICG-1)
> Forschungszentrum Juelich
> email: R.Bauer@fz-juelich.de
> http://www.fz-juelich.de/icg/icg1/
> ============================================================ ======
> a IDL library at ForschungsZentrum Juelich
> http://www.fz-juelich.de/icg/icg1/idl_icglib/idl_lib_intro.h tml
>
> http://www.fz-juelich.de/zb/text/publikation/juel3786.html
> ============================================================ ======
>
> read something about linux / windows
> http://www.suse.de/de/news/hotnews/MS.html
Ok, thanx.
I prefer the de defsysv method.
--
+- - - - - - - - - - - - - - - - - - - - - - - -+
| Miguel Angel C�rdoba cordoba@ehma.upc.es |
| |
| http://campus.uab.es/~2034008 |
| |
| Grup de Modelitzaci� Hidrometeorol�gica (UPC) |
| (http://www.upc.es/ehma/gmh) |
+- - - - - - - - - - - - - - - - - - - - - - - -+
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| Re: Global Variable [message #26835 is a reply to message #19399] |
Mon, 01 October 2001 02:53 |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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Martin Downing wrote:
>
> First comment is to only use global variables sparingly, sometimes they are
> appropriate but try not to rely on them to make programming simpler.
> I know of three ways, the SYSTEM variables are fully global, and may be user
> defined, COMMON BLOCK variables are shared between those routines which
> include a
> declaration for the common block, these are very suitable for those programs
> where you cant find a way of writing your code without creating global
> variables, but do not want the variables to be seen by any old routine.
>
> system variable eg:
> ------------
> IDL>filepaths = {tag:"FILEPATHS", bin:bin)
> IDL>defsysv, '!fpaths',filepaths ; a variable for local paths
>
> now you can use this variable from anywhere in your code as:
>
> IDL> print, !fpaths.bin
> d:\martin\bin\
> ------------
>
> For common block variables you need a block identifier then a list of
> variables in the block. Note that the order is all that is relevent and that
> the first declaration defines the size of the block: eg
>
> pro foo
> COMMON FOO_COMMON_VARIABLES, a,b,c,d
> a = "first"
> b="second"
> c="third"
> d="fourth"
> print_foo
> end
>
> pro print_foo
> ; note later calls do not have to decare all block variables
> COMMON FOO_COMMON_VARIABLES, d,c,var3
> print, d
> print, c,
> print, var3
> end
>
> the result of calling this procedure is demonstrates that there is no
> association between variable names inthe common block just the variable
> order.
> IDL> foo
> first
> second
> third
>
> ------------------------------
> Lastly there is a *really* nice way of passing around all the 'global'
> variables you need in your widget programs using get/set_uvalue which. This
> is my favourite tip learnt from David's books so I shall leave him to
> describe. In essence you call:
> WIDGET_CONTROL, base, SET_UVALUE=info_structure
> WIDGET_CONTROL, event.top, GET_UVALUE=info_structure
>
> cheers
>
The fourth way is to use Pointers
value=10
ptr=ptr_new(value)
help, *ptr
Reimar
--
Reimar Bauer
Institut fuer Stratosphaerische Chemie (ICG-1)
Forschungszentrum Juelich
email: R.Bauer@fz-juelich.de
http://www.fz-juelich.de/icg/icg1/
============================================================ ======
a IDL library at ForschungsZentrum Juelich
http://www.fz-juelich.de/icg/icg1/idl_icglib/idl_lib_intro.h tml
http://www.fz-juelich.de/zb/text/publikation/juel3786.html
============================================================ ======
read something about linux / windows
http://www.suse.de/de/news/hotnews/MS.html
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| Re: Global Variable [message #26836 is a reply to message #19399] |
Mon, 01 October 2001 02:40 |
Martin Downing
Messages: 136
Registered: September 1998
|
Senior Member |
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First comment is to only use global variables sparingly, sometimes they are
appropriate but try not to rely on them to make programming simpler.
I know of three ways, the SYSTEM variables are fully global, and may be user
defined, COMMON BLOCK variables are shared between those routines which
include a
declaration for the common block, these are very suitable for those programs
where you cant find a way of writing your code without creating global
variables, but do not want the variables to be seen by any old routine.
system variable eg:
------------
IDL>filepaths = {tag:"FILEPATHS", bin:bin)
IDL>defsysv, '!fpaths',filepaths ; a variable for local paths
now you can use this variable from anywhere in your code as:
IDL> print, !fpaths.bin
d:\martin\bin\
------------
For common block variables you need a block identifier then a list of
variables in the block. Note that the order is all that is relevent and that
the first declaration defines the size of the block: eg
pro foo
COMMON FOO_COMMON_VARIABLES, a,b,c,d
a = "first"
b="second"
c="third"
d="fourth"
print_foo
end
pro print_foo
; note later calls do not have to decare all block variables
COMMON FOO_COMMON_VARIABLES, d,c,var3
print, d
print, c,
print, var3
end
the result of calling this procedure is demonstrates that there is no
association between variable names inthe common block just the variable
order.
IDL> foo
first
second
third
------------------------------
Lastly there is a *really* nice way of passing around all the 'global'
variables you need in your widget programs using get/set_uvalue which. This
is my favourite tip learnt from David's books so I shall leave him to
describe. In essence you call:
WIDGET_CONTROL, base, SET_UVALUE=info_structure
WIDGET_CONTROL, event.top, GET_UVALUE=info_structure
cheers
Martin
----------------------------------------
Martin Downing,
Clinical Research Physicist,
Orthopaedic RSA Research Centre,
Woodend Hospital, Aberdeen, AB15 6LS.
"Miguel �ngel C�rdoba" <cordoba@ehma.upc.es> wrote in message
news:3BB82DB7.265E2670@ehma.upc.es...
> Anybody know how can I define al global variable?.
>
> Thanx.
>
> --
> +- - - - - - - - - - - - - - - - - - - - - - - -+
> | Miguel Angel C�rdoba cordoba@ehma.upc.es |
> | |
> | http://campus.uab.es/~2034008 |
> | |
> | Grup de Modelitzaci� Hidrometeorol�gica (UPC) |
> | (http://www.upc.es/ehma/gmh) |
> +- - - - - - - - - - - - - - - - - - - - - - - -+
>
>
>
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